High strength al-cu-mg-ag-si alloy for structural applications

ABSTRACT

The present invention relates generally to aluminum-copper-magnesium based alloys and products, and more particularly to aluminum-copper-magnesium-Silver-Silicon based alloys and products particularly suitable for aircraft structural applications and military vehicle structural applications requiring very high strength and ductility.

CROSS REFERENCES TO OTHER APPLICATIONS

This application claims priority from U.S. Provisional Application Ser. No. 61/573,782 filed on Sep. 12, 2011 and U.S. Provisional Application Ser. No. 61/626,790 filed on Oct. 3, 2011 bothl of which are incorporated by reference herein in their entirety. Reference to documents made in the specification is intended to result in such patents or literature cited are expressly incorporated herein by reference, including any patents or other literature references cited within such documents as if fully set forth in this specification.

This application is part of a government project. The research leading to this invention was supported by a Grant Number W911NF-07-2-0073 from the U.S. ARMY. The United States Government retains certain rights in this invention.

BACKGROUND INFORMATION OF THE INVENTION

1. Field of Invention

The present invention relates generally to aluminum-copper-magnesium based alloys and products, and more particularly to aluminum-copper-magnesium-silver-silicon based alloys and products particularly suitable for aircraft structural applications and military vehicle structural applications requiring very high strength and ductility.

2. Description of Related Art

Aluminum alloys containing copper, magnesium and silver are known in the art.

U.S. Pat. No. 4,772,342 describes a wrought aluminum-copper-magnesium-silver alloy including copper in the amount of 5.7 weight (wt.) percent (%), magnesium in an amount of 0.3-0.8 wt. %, silver in an amount of 0.2-1 wt. %, manganese in an amount of 0.3-1.0 wt. %, zirconium in an amount of 0.1-0.25 wt. %, vanadium in an amount of 0.05-0.15 wt. %, silicon less than 0.10 wt. %, and the balance aluminum.

U.S. Pat. No. 5,376,192 discloses a wrought aluminum alloy comprising about 2.5-5.5 wt. % copper, about 0.10-2.3 wt. % magnesium, about 0.1-1.0 wt. % silver, up to 0.05wt. % titanium and the balance aluminum, in which the amount of copper and magnesium together is maintained at less than the solid solubility limit for copper and magnesium in aluminum.

U.S. Pat. Nos. 5,630,889, 5,665,306, 5,800,927, and 5,879,475 disclose substantially vanadium-free aluminum-based alloys including about 4.85-5.3 wt. % copper, about 0.5-1 wt. % magnesium, about 0.4-0.8 wt. % manganese, about 0.2-0.8 wt. % silver, up to about 0.25 wt. % zirconium, up to about 0.1 wt. % silicon, and up to 0.1 wt. % iron, the balance aluminum, incidental elements and impurities. The alloy can be produced for use in extruded, rolled or forged products, and in a preferred embodiment, the alloy contains a Zr level of about 0.15 wt. %.

SUMMARY OF THE INVENTION

An object of the present invention was to provide a high strength, high ductility alloy, comprising copper, magnesium, silver, manganese, silicon and optionally dispersoid forming elements.

In accordance with the present invention, there is provided an aluminum-copper alloy comprising about 4.5- 6.8 wt. % copper, 0.1-1.8 wt. % magnesium, 0.1-0.8 wt. % silver, 0.0-1.2 wt. % manganese, 0.25-1.2 wt. % silicon, the balance being aluminum and incidental elements and impurities such as, not limited to, iron up to 0.5%, zinc up to 0.5% and nickel up to 0.5 wt. %. Optionally one or more dispersoid forming elements selected from the group consisting of Titanium, Zirconium, Chromium, Scandium and Vanadium may be added in an amount of up to 0.5 wt. % for titanium, 0.25 wt. % for zirconium, 0.5 wt. % for Cr, 0.5 wt. %, 0.8 wt. % for Sc, and 0.2 wt. % for V.

The inventive alloy can be manufactured and/or treated in any desired manner, such as by forming an extruded, rolled, or forged product. The present invention is further directed to methods for the manufacture and use of alloys as well as to products comprising alloys.

Additional objects, features, and advantages of the invention will be set forth in the description which follows, and in part, will be obvious from the description, or may be learned by practice of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

The high strength AL—CU—MG—AG—SI ALLOY for structural applications comprises a, high ductility alloy, comprising copper, magnesium, silver, manganese, silicon and optionally dispersoid forming elements.

One preferred embodiment of an aluminum-copper alloy comprises about 4.5- 6.8 wt. % copper, 0.1-1.8 wt. % magnesium, 0.1-0.8 wt. % silver, 0.0-1.2 wt. % manganese, 0.25-1.2 wt. % silicon, the balance being aluminum and incidental elements and impurities such as, not limited to, iron up to 0.5%, zinc up to 0.5% and nickel up to 0.5 wt. %. Optionally one or more dispersoid forming elements selected from the group consisting of Titanium, Zirconium, Chromium, Scandium and Vanadium may be added in an amount of up to 0.5% for titanium, 0.25% for zirconium, 0.5 wt. % for Cr, 1.0 wt. %. 0.8 wt. % for Sc, and 0.2 wt. % for V.

The following examples describe preferred embodiments of the invention. Other embodiments within the scope of the claims herein will be apparent to one skilled in the art from consideration of the specification or practice of the invention as disclosed herein. It is intended that the specification, together with the examples, be considered exemplary only, with the scope and spirit of the invention being indicated by the claims which follow the examples. In the examples all percentages are given on a weight basis unless otherwise indicated.

Reference to documents made in the specification is intended to result in such patents or literature cited are expressly incorporated herein by reference, including any patents or other literature references cited within such documents as if fully set forth in this specification.

These and other objects of the present invention will be more fully understood from the following description of the invention.

EXAMPLE 1

Large commercial scale ingots were cast with 16 inch thick by 45 inch wide cross section for the AA2139 alloy chemistry shown in the table 1:

TABLE 1 CHEMISTRY OF 2139 ALLOY INGOT Si Fe Cu Mn Mg Zn Ti Zr Ag 0.050 0.088 4.913 0.332 0.457 0.039 0.110 0.004 0.343 0.051 0.088 4.879 0.294 0.442 0.033 0.094 0.001 0.345

AA2139 Registered Chemical Limits in Weight %:

-   Cu; 4.5-5.5 -   Mn; 0.2-0.6 -   Mg; 0.2-0.6 -   Ag; 0.15-0.6 -   Zn; 0.25 max -   Si; 0.10 max -   Fe; 0.15 max -   Ti; 0.15 max -   Other; 0.05 max (EACH) -   Other; 0.15 max (total) -   Aluminum; Remainder

This ingot was homogenized at a temperature of 970 degree F. for 24 hours. The ingot was hot rolled to 2.0″ gauge plate. Hot rolling said ingot at a temperature range of 700 to 900 degree F. until it forms a plate of 2″ gauge plate. The plate was solution heat treated at 980 degree F. for 1 hour, followed by cold water quench.

This plate was cut into two plate; Plate S1 and Plate S2.

Plate S1 was received age treatment of 48 hours at 320 degree F. to achieve peak strength to 2139-T6 temper product.

The tensile test result of this plate (2139-T6 temper) is shown below.

Plate S2 was received 6% cold work by stretch, then received age treatment of 24 hours at 320 degree F. to achieve peak strength to 2139-T8 temper product. The tensile test result of this plate (2139-T8 temper) is also shown below.

The result clearly show the effect of cold work on the mechanical property of AA2139 in (longitudinal) direction by comparing the tensile test results from the Plate S1 (2139-T6 temper) and Plate S2 (2139-T8 temper)

TABLE 2 Tensile Properties of AA2139 in T6 and T8 temper in Longitudinal direction 0.2% Yield Ultimate Stress Strength Elongation Plate S1; 2139-T6 63.4 ksi 68.5 ksi 10.4% (with 0% cold work) Plate S2; 2139-T8 65.1 ksi 70.2 ksi  14% (with 6% cold work)

EXAMPLE 2

AA2014 is known one of the best Aluminum alloy based on Al—Cu—Mg based aluminum alloy having high strength in T6 temper condition(i.e., age hardening treatment with 0% prior cold work) and widely used in aerospace structural applications.

AA2139 Registered Chemical Limits in Weight %:

-   Cu; 3.9-5.0 -   Mn; 0.4-1.2 -   Mg; 0.2-0.8 -   Ag; none -   Zn; 0.25 max -   Si; 0.5-1.2 -   Fe; 0.7 max -   Ti; 0.15 max -   Cr; 0.1 max -   Other; 0.05 max (EACH) -   Other; 0.15 max (total) -   Aluminum; Remainder

According to the Aerospace Material Specification (AMS 4133), the minimum tensile properties in hand forgings from the product thickness up to 2 inches, are listed as follows:

TABLE 3 MINIMUM TENSILE PROPERTIES OF AA2014-T6 0.2% Yield Ultimate Tensile Test Direction Stress Strength Elongation Longitudinal 56 ksi 65 ksi 8% Long Transverse 56 ksi 65 ksi 3%

According to the ASM Aerospace Specification for Aluminum 2014-T6; 2014-T651, the typical tensile properties are shown in TABLE 4 below:

TABLE 4 TYPICAL TENSILE PROPERTIES OF 2014-T6 0.2% Yield Ultimate Tensile Test Direction Stress Strength Elongation Longitudinal 60 ksi 70 ksi 13%

EXAMPLE 3 Invented Alloy (Alloy A)

Laboratory scale ingot (Alloy AT-1)was cast with 2 inch thick by 5 inch wide by 15 inch long ingot. The alloy chemistry is shown in the TABLE 5:

TABLE 5 CHEMISTRY OF THE INVENTED ALLOY (Alloy A) Alloy No. Cu Mg Mn Fe Si Ti Zr Ag A 5.1 0.4 0.37 0.06 0.3 0.04 0.02 0.35 (all chemistries are in wt. %)

This ingot was homogenized at a temperature of 950 degree F. for 24 hours. The ingot was forged 0.5″ gauge thick hand forged product. Hot hand forging said the ingot was forged at a temperature range of 850 to 700 degree F. until it forms to 0.5″ thick. The 0.5 inch gauge forged plate was solution heat treated at 950 degree F. for 2 hours, followed by cold water quench. The water quenched product was divided into two pieces, piece-A1 and piece-A2.

A1 was age hardened for 4 hours at 350 deg F. A2 was age hardened for 32 hours at 320 deg The test results from the aged material are shown in Table 6:

TABLE 6 TENSILE PROPERTIES OF THE INVENTED ALLOY (Alloy A) in T6 temper (0% stretch prior to age hardening process) 0.2% Yield Ultimate Tensile Sample ID Test Direction Stress Strength Elongation A1 Longitudinal 67.6 ksi 73.7 ksi 13.5% A2 Longitudinal 69.0 ksi 74.9 ksi 10.4%

The comparison of the longitudinal direction tensile properties of the invented alloy (Alloy A) to AA2139 and AA2014 in Table 7 demonstrated the high strength advantage of the inventive alloy (Alloy A) in -T6 temper condition. The tensile strength of the Inventive Alloy (Alloy A) in T6 temper condition is even higher than that of AA2139 in T8 temper condition.

TABLE 7 Comparison of Tensile Properties of Invented alloy (Alloy A) to AA2139 and AA2014 in Longitudinal direction 0.2% Yield Ultimate Stress Strength Elongation Plate S1; 2139-T6 63.4 ksi 68.5 ksi 10.4% (with 0% cold work) Plate S2; 2139-T8 65.1 ksi 70.2 ksi  14% (with 6% cold work) Typical, 2014-T6  60 ksi  70 ksi  13% (with 0% cold work) Invented Alloy A1-T6 67.6 ksi 73.7 ksi 13.5% (with 0% cold work) Invented Alloy A2-T6 69.0 ksi 75.9 ksi 10.4% (with 0% cold work)

The foregoing detailed description is given primarily for clear understanding of the new alloy composition and no unnecessary limitations are to be understood therefrom, for modifications will become obvious to those skilled in the art based upon more recent disclosures and may be made without departing from the spirit of the invention and scope of the appended claims. 

I claim:
 1. An alloy comprising from about 4.0-6.0 wt. % copper, from about 0.1-1.8 wt. % magnesium, from about 0.0-0.8 wt. % silver, from about 0.0-0.8 wt. % manganese, from about 0.1-1.2 silicon, and from about 0.0-0.12 titanium and the balance being aluminum and incidental elements and impurities.
 2. The alloy of claim 1, wherein said incidental element and impurities can includes iron.
 3. The alloy of claim 1, further comprising one or more dispersoid forming elements selected from the group consisting of chromium, zirconium, scandium and vanadium and combinations thereof.
 4. The alloy of claim 1, further comprising chromium in an amount of up to 0.8 wt. %, scandium in an amount up to 0.8 wt. %, and vanadium in an amount of up to 0.2 wt. % either in addition to, or instead of titanium.
 5. The alloy of claim 1 exhibit very high strength when the alloy is processed to wrought product for engineering structural applications having surprisingly high strength in T6 temper product (i.e., no cold work or very low amount of cold work prior to final age strengthening step on the product of cold water quenched after solution heat treatment)
 6. The alloy of claim 1 is suitable for T8 temper application with even more pronounced high strength capability for engineering structural applications. 